1. Field of the Invention
This invention relates to an improved electrode arrangement for use in an electrostatic precipitator that aids the efficient collection and elimination of dusts and mists from industrial effluent gases before they are released to the atmosphere.
2. Description of the Prior Art
The efficient collection and removal of the many and various dusts and mists that are found in industrial gases has always been the goal of and is the basis for continued improvements in the electrostatic precipitator field.
Since the pioneering work of Cottrell, the conventional electrostatic precipitator has utilized an electrical corona between two electrodes for the charging and collection of dusts and mists. However, the use of such a method results in inefficiency in particle charging. This inefficiency is particularly apparent when the electrical corona is used for charging dusts and mists which have a very high resistivity (greater than 1.times.10.sup.11 ohn-cm).
A more recent development exemplified by the invention in U.S. Pat. No. 4,056,372 to T. Hayashi separated the charging region from a corona-free collection region. This development greatly enhanced the energy efficiency of the electrostatic precipitator. However, some very high resistivity dusts remained difficult to collect.
Some improvement in collecting the harder to collect dusts has also been achieved by adding stages of collection in series with respect to the direction of gas flow, each stage consisting of an electrostatic precipitator for example of the Hayashi type. Large industrial assemblies with as many as 4 or 5 stages are routinely offered by the industry with only partial success in treating the very high resistivity dusts. Such large multi-staged electrostatic precipitators are very costly and take up large amounts of space around industrial plants. This problem is particularly acute at many older plants which have little or no space remaining in which to locate the now required air pollution control equipment for which they were never originally designed.
Electrostatic precipitators of the type to which the present improvement pertains are referred to as being of the parallel plate type. Such an electrostatic precipitator has a collection region that comprises a pack of parallel equally spaced plates suspended so they are parallel to the direction of gas flow through the electrostatic precipitator chamber or plenum. Each plate thus has a leading and trailing edge which are respectively the upstream and downstream edges of the plate as defined by the direction of gas flow. This pack of plates is further divided into two sets of plates such that every other plate belongs to the same set. Each set is maintained at a different electrical potential by a D.C. power source so that every plate (except those forming the outer boundaries of the plate pack nearest the walls of the plenum) is adjacent to two plates of a potential different from itself; those latter two plates thus described being at the same potential. This produces an electrostatic field between every pair of adjacent plates.
Particle collection is the product of two phenomena, both of which involve moving the particle to a collection surface. One phenomenon is the electrical wind of ions that transfers its momentum in the direction of a charged collection surface to the particles regardless of the charge on the particle itself. In the field of this invention this is called the hydrodynamic effect. In the second phenomenon, the particle itself is charged in the electrical corona which charge then allows the particle to be attracted to a collection plate of opposite polarity with respect to the charge on the particle. Without this charge, the particle is not acted upon by the electrical field in the collection region of the electrostatic precipitator.
Recent work has focused its attention on improved particle charging. This work has involved establishment of wholly separate charging and collection regions as exemplified by U.S. Pat. No. 3,803,808 to Shibuya et al. and the subsequent enlargement of the charging region. Again, this approach was only partially successful, and space utilization remained a distinct problem.